1. Field of the Invention
This invention is in the field of progressive fin dies.
2. Description of the Prior Art
Many heat transfer devices include plate type heat transfer fins having collared holes through which coolant tubes extend. The collared holes are produced by progressive fin dies which successively strike the fin to first draw the bonnet and then pierce and straighten the collar. The collared holes are then reflared with the fins then being cut and trimmed to the desired configuration.
The fin will normally stick in the straightening bushing as the ram is withdrawn unless an ejector or stripper is provided for forcing the fin from the punch. An ejector is shown in the U.S. Pat. No. 2,772,735 issued to R. L. Wakelee. The prior art ejectors leave a dimple in the relatively thin fin workpiece providing an undesirable appearance. Disclosed herein are two different embodiments of a stripper which contact the top edge of the collared holes in such a manner so as to leave the fin free of the dimples or marks and providing a blemish-free fin surface.
It is known to provide a compound collar straightening and piercing die. The prior art dies provide a pierce punch which is movable to and from a pierce bushing which extends into the bonnet. Simultaneously, a straightening bushing encircling the pierce punch is provided for externally engaging and straightening the collar. Metal particles accumulate between the pierce punch and the straightening bushing in the prior art devices since the pierce punch is spaced inwardly from the straightening bushing. Disclosed herein is a compound collar straightening and pierce die having a stripper bushing filling the space between the pierce punch and the straightening bushing preventing accumulation of metal particles and providing a self-cleaning pierce punch. Patents of interest in this field are the following: Nos. 2,763,228 issued to P. J. Lawson 3,146,749 issued to C. W. Heinle 3,367,164 issued to L. A. Franks et al